Electrodeposition as a coating application method involves deposition of a film-forming composition onto a conductive substrate under the influence of an applied electrical potential. Electrodeposition has become standard in the coatings industry because, by comparison with non-electrophoretic coating means, electrodeposition offers increased paint utilization with less waste, improved corrosion protection to the substrate, and minimal environmental contamination.
Initially, electrodeposition was conducted with the workpiece to be coated serving as the anode. This was familiarly referred to as anionic electrodeposition. However, in 1972 cationic electrodeposition was introduced commercially and has become an industry standard. Today, cationic electrodeposition is by far the prevalent method of electrodeposition. In fact, a cationic primer coating is applied by electrodeposition to more than 80 percent of all motor vehicles produced throughout the world.
Electrodepositable coatings typically contain pigments that serve numerous purposes. Usually, the pigments are introduced into the coatings after incorporation into a grinding vehicle by a milling process. The use of a grinding vehicle reduces pigment agglomeration and allows for homogeneous dispersion of the pigment into the coating bulk, but it involves additional formulation steps at a higher cost. It also makes it difficult to incorporate a high level of pigment into the coating and weakens the corrosion barrier properties of the coating by lowering the pigment-to-binder (P:B) ratio and crosslink density of the coating.
There remains a need in the coatings industry for a cost effective electrodepositable primer composition which allows for higher pigment loadings, to provide improved corrosion resistance to a metal substrate.